EVALUATION OF FOLIAR INSECTICIDES FOR THE CONTROL OF COLORADO POTATO BEETLE AND POTATO LEAFHOPPER IN POTATOES IN VIRGINIA, 2009
Arthropod Management Tests
Hélène Doughty Colorado potato beetle (CPB): Leptinotarsa decemlineata (Say) Potato leafhopper (PLH): Empoasca fabae (Harris) The objective of this experiment was to assess the efficacy of various foliar insecticides to control CPB on potatoes. The trial consisted of 13 treatments arranged in a RCB design with four replicates. Potatoes were planted on 24 Mar, 2009 at the Virginia Tech Eastern Shore AREC near Painter, VA. Plots were 2 row wide and 20 ft (6.1 m) long with unplanted guard rows on
... nted guard rows on each side. Rows were planted on a 3 ft row center (0.9 m) with 11 inches (0.3 m) between plants, in a 6 tier field design with 8 ft (2.4 m) alleys between tiers and a 16 ft (4.9 m) center alley. Insecticide treatments were applied at 38 gpa using a 4-nozzle boom equipped with 110003VS spray tips spaced 20 inches apart, spraying 2 rows at a time, and powered by a CO 2 backpack sprayer set at 40 psi. All seed pieces were treated with 8% alder bark at 16 oz / cwt. All insecticide treatments were applied twice (on 19 and 26 May) after CPB eggs had hatched and small larvae were feeding. All plots were maintained according to standard commercial practices. Numbers of CPB small larvae (1 st and 2 nd instars), large larvae (3 rd and 4 th instars), and adults were counted on 10 randomly picked stems per plot on 22 (3 DAT), 26 May (7 DAT), and 1 Jun (6 DAT2). F2 generation adult CPB were counted on 5 randomly picked stems per plot on 11 Jun (16 DAT2). On 1 Jun (6 DAT2), PLH nymphs were counted on 10 randomly picked, fully expanded compound leaves per plot. On 8 Jun, plots were visually assessed for % defoliation from CPB. On 30 Jun, potato tubers were mechanically harvested from each two-row plot, graded to size (Chef, Large A, Small A, and B), and weighed. All data were analyzed using ANOVA. Proportion data were arcsine square root transformed prior to analysis. Means were separated using Fisher's Protected LSD at the 0.05 level of significance. CPB pressure was high with an average of 180 larvae (small and large) per 10 vines prior to the first application of insecticides. All insecticide treatments provided some level of CPB control as evidenced by significantly fewer beetle life stages on plants and % defoliation. The best control of CPB was provided by the higher rates of HGW86 10OD, Provado, Coragen, and Alverde. All treatments of HGW86 10OD provided significant control of CPB at all dates except at the 13.5 fl. oz rate without MSO on 22 May (3 DAT) and 26 May (7 DAT). The plots containing this particular treatment were located at the edge of the field and/or near untreated plots and may have experienced higher pest pressure at times. This observation was reflected in the defoliation ratings. All treatments of HGW86 also provided significant control of F2 generation CPB adults at 16 DAT2. All rates of Coragen 20SC had significantly lower numbers of CPB compared to the untreated check except at the 5 fl. oz rate on 22 May (3 DAT) for small larvae. . Although significantly better than the untreated check, Movento was not as efficacious at controlling CPB as the other insecticides and was originally included in the trial to test for efficacy against potato aphids. PLH pest pressure was moderate, and there was a significant treatment effect on numbers of nymphs on leaves 6 DAT2. All HGW86 treatments (except HGW86 at the 13.5 fl. oz rate without MSO) as well as both rates of Movento and Alverde provided significant control of PLH. Coragen did not appear efficacious against that pest. Provado did not provide effective control of PLH either. No visible signs of phytotoxicity were observed from any treatment.